1. Technical Field
The present invention relates to charging systems in general, and in particular to a method for controlling a charging system having multiple loads.
2. Description of Related Art
A notebook-type portable computer (notebook PC) has a relatively simple system configuration when being used in a mobile environment in order to achieve a light weight or prolong a battery-powered operating time. On the other hand, when being used in an office environment, the notebook PC can be connected to a function extending apparatus known as a docking station (or a port replicator) so that a user can utilize the features and capabilities corresponding to a desktop computer. The notebook PC is generally equipped with a charger, and in some cases, a special charger is also mounted on the function extending apparatus. Therefore, the user is able to carry and use a battery charged by the function extending apparatus with the notebook PC as an auxiliary battery.
When the notebook PC is being used while connected to a function extending apparatus, an AC/DC adapter is not connected directly to the notebook PC but the AC/DC adapter is preliminarily connected to the function extending apparatus supplies power to a system load of the notebook PC, a charger of the notebook PC, a system load of the function extending apparatus, and a charger of the function extending apparatus. Among all system loads, a central processing unit (CPU) exhibits the largest maximum power consumption. The AC/DC adapter has rated power suitable for the maximum power consumption of all system loads including the CPU. The variation in the power consumption of the system loads is severe, and charging the battery by means of the charger is not always an urgent task. Therefore, when the rated power of the AC/DC adapter is set to be larger than the sum of the total maximum power consumption of the system load and the maximum power consumption of the charger, the utilization rate of the AC/DC adapter may decrease, and thus, the battery is overcharged.
Therefore, the charging of the battery by means of the charger is generally carried out by using surplus power, which is the difference between the rated power of the AC/DC adapter and the power consumption of the system load. When the notebook PC is being used while connected to the function extending apparatus, power is supplied from the AC/DC adapter connected to the function extending apparatus, to the system load of the notebook PC, the system load of the function extending apparatus, and the charger of the notebook PC. However, depending on the overall power consumption or the output power of the AC/DC adapter, it may be necessary to limit the power consumption of any of the system loads.
In a computer system, generally, without limiting the power consumption of the system load, when the power consumption of the system load increases, the power consumption of both or either one of the charger of the notebook PC and the charger of the function extending apparatus is limited. One method is by measuring power consumption of a charger mounted on a notebook PC and power consumption of a charger mounted on a function extending apparatus and then controlling the power consumption of both or either one of the chargers based on the measurement result. Specifically, a configuration may be considered in which when output power of an AC/DC adapter exceeds a predetermined value, the power consumption of the charger of the notebook PC is compared with the power consumption of the charger of the function extending apparatus so that the larger power consumption is limited.
However, with the above-mentioned method, in order to limit the power consumption of the charger of the notebook PC or the charger of the function extending apparatus, it is necessary to acquire information regarding the power consumption of both chargers. The AC/DC adapter needs to supply power to the function extending apparatus connected to the notebook PC or the function extending apparatus not connected to the notebook PC. Therefore, when the notebook PC is not connected to the function extending apparatus, it is impossible to acquire information of the charger of the notebook PC, and thus, it is difficult to employ the above-mentioned method. However, when the notebook PC is being used without the function extending apparatus, as long as the battery mounted on the notebook PC is more sufficiently charged than the battery mounted on the function extending apparatus, it would be very convenient because a user is able to use the notebook PC in a mobile environment without the need to replace the battery. Therefore, it would be helpful to reduce the power consumption of the charger mounted on the function extending apparatus first or stop the charger when controlling the power consumption of the charger.
Various safety measures are taken to ensure safe charging of a secondary battery. For example, when a battery voltage decreases, a method is employed in which pre-charging is first performed with a very small current and then transitions to a normal charging mode. In this case, when the battery voltage is not recovered by the pre-charging within predetermined consecutive intervals of time, a safety device is operated so that the charging is temporarily stopped. Therefore, there is a possibility that the charger mounted on the function extending apparatus is stopped, and thus, the pre-charging is not completed within a predetermined period of time. In such a case, a user may need to perform a reset operation, and thus, the charging operation becomes complicated.